Method of making hollow sheet metal fabrications having a plurality of interconnected passageways



Sept. 28, 1954 H. GRENELL ,6

METHOD OF MAKING HOLLOW SHEET METAL FABRICATIONS HAVING A PLURALITY 0F INTERCONNECTED PASSAGEWAYS Filed Nov. 18, 1949 2 Sheets-Sheet l Figi Fig.2

INVENTOR LELAND IHL GRIENELL BY {M 8.11%

ATTORNEY p 28, 1954 L. H. GRENELL 2,690,002

METHOD OF MAKING HOLLOW SHEET METAL FABRICATIONS HAVING A PLURALITY OF INTERCONNECTED PASSAGEWAYS Filed Nov. 18, 1949 2 Sheets-Sheet 2 Fig.6

INVENTOR LELAND) Ho GRIENIELL wiw ATTORNEY water Patented Sept. 28, 1954 METHOD OF MAKING HOLLOW SHEET METAL FABRICATIONS HAVING A PLU- RALITY OF INTER-CONNECTED PAS- SAGEWAYS Leland H. Grenell, Pasadena Hills, Mm, assignor to Olin Industries, Inc., East Alton, EL, a corporation of Delaware Application November 18, 1949, Serial No. 128,116

Claims. (01. 29157.3)

This invention relates to the manufacture of sheet metal fabrications and in particular to structural members, heat exchangers, fluid containers, and the like made of sheet metal and to a method of making the same.

Structural members for some uses must have at least one flat or smooth surface, for instance, when used as airplane fuselage, wing, or tail surfaces, box car walls, and the like, and it has been customary to utilize two metal sheets face to face, one flat and one indented, riveted, spotwelded, or brazed together. In such composite members, the ribs or bulges of the indented sheet strengthen and stiffen the flat sheet and thereby reinforce the member. In the art of making refrigerator evapcrators, radiant heaters, and the like, such heat exchange devices in general are composed of a plurality of tubes or chambers adapted to serve as a conduit for the fluid of the heat exchange system and have been constructed heretofore of relatively thin gauge sheet metal by a method which involves indenting channels or grooves in the metal sheeting in a pattern designed to provide after assembly interconnecting passageways. Two of the sheets are then arranged face to face in superposed relation and joined together by brazing or spotwelding along predetermined lines to provide the desired fluid passageways between the sheets. Another method for making heat exchange devices, disclosed in U. S. Patent 1,779,911 issued to Litie, October 28, 1930, consists briefly in superposing two sheets of metal, sealing the edges of the sheets by welding, joining the inner faces of the sheets at spaced intervals by spot-welding, and then introducing fluid pressure through a hole in one of the sheets to expand and separate the sheets between the spot-welds.

Now, the brazing, riveting and spot-welding methods utilized in producing such fabrications have attendant disadvantages. For instance, when the sheets are joined by brazing, one must employ a brazing alloy and an extra processing step of inserting and adequately positioning the brazing strip is required. Further, the brazed joint is not always mechanically perfect and the sheets may separate when stress is applied. Likewise any strengthening of the tube or rib walls due to working is lost owing to, the annealing effect obtained at the brazing temperature. The spot-welding and riveting techniques are not adapted for complete sealing of the sheets between the ribs or fluid passageways, particularly when the ribs or passages are formed by long ducts following either straight, or serpentine,

tortuous or other intricate paths. With such structures, voids are often found present between the sheets at points other than the intended ribs or passageways, resulting in possible lower strength in the case of structural members, and in leaks in the case of heat exchangers, and otherwise detract from the efficiency of such fabrications. Further the coarse-grained cast structure of the spot-welds tends to weaken, the fabrication at these points. Likewise, the spotwelding procedure is not in general well suited for alloys of high electrical conductivity and in many instances the surfaces of the sheets tend to adhere to the spot-welding electrodes marring the sheets and requiring frequent cleaning of the electrodes.

It is therefore an object of this invention to provide an economical, eihcient method for manufacturing such sheet metal fabrications free of the limitations and disadvantages set forth in the foregoing; Another object of the invention is to provide an economical method for manufacturing heat exchange devices from sheet metal of either high or low electrical conductivity, which method permits complex duct patterns or conduit systems to be utilized without the hazards of fluid leaks. Still another object is to provide a relatively low cost thermally efficient heat exchange device. A further object is to provide a low cost method of forming relatively strong structural members, fluid containers, and other such devices from metal sheeting. A still further object is to provide a relatively low cost, light weight, strong sheet metal structural member.

The foregoing objects and advantages, as well as others which may become apparent from the detail description hereinafter, are accomplished in accordance with this invention by a combination of processing steps including sandwiching a pattern of a non-bonding or separation material between two sheets of metal, forming a single layer of metal between the areas covered by the separation material by pressure welding, and applying a fluid pressure on the inner surfaces held apart by the separation material to expand the metal in these areas. Any desired processing maybe employed intermediate the aforenamed steps provided suchprocessing does not interfere with the functioning of said steps. The diameter, length, and positioning of the cavities formed within the sheet by the fluid pressure and the resulting bulges or ribs on the surface depend mainly upon the pattern dimensions and design in which the separation material is originally applied and complex and intricately shaped reinforcing ribs or conduits are thus readily formed by applying the desired pattern. No voids exist between adjacent passageways or ribs, since the metal of the sheets intermediate the passageways are forged or pressure welded into one layer of metal of substantially uniform composition.

Having described in the foregoing in a general way the nature and substance of this invention, there follows a more detailed description of preferred embodiments thereof with reference to the accompanying drawing in which:

Figure l is a plan view illustrating a sheet of metal coated with a pattern of separation material,

Figure 2 is a plan View illustrating a sheet of metal to be superposed on the coated sheet of Figure 1,

Figure 3 is an end view illustrating the metal sheets of Figures 1 and 2 after assembly,

Figure 4 is a perspective view illustrating the assembly of Figure 3 after hot rolling,

Figure 5 is an enlarged sectional View illustrating the metal sheet at BB of Figure 4,

Figure 6 is a plan view illustrating reinforced metal sheeting suitable for use as a heat exchanger,

Figure 7 is a sectional view taken at AA in Figure 6,

Figure 8 is a sectional view illustrating another embodiment, in which the sheet has ribs only on one surface,

Figure 9 is a sectional view illustrating a metal sheet held in a die,

Figure 10 is a sectional view illustrating a sheet formed in accordance with this invention,

Figure 11 is a plan view illustrating another embodiment, in which the ribs are on one surface of the sheet in one area and on the opposite surface in another area, and

Figure 12 is a cross-sectional view of the sheet of Figure 11.

Referring first to Figures 1 and 2, for the manufacture of a heat exchange device, sheets 1 and 2 of metal, 0.070 inch thick and composed of 92% to 94% copper, 2.05% to 2.60% iron, 0.025% phosphorus, 0.05% lead, with the balance zinc, are first degreased by immersion in an organic solvent bath, such as naphtha or white gasoline, at room temperature and then wiped free of solvent. The sheets are then cleaned in an acid bath containing approximately 1 part by volume of 68% nitric acid, 1 part by volume of 95% sulphuric acid, and 1 part by volume of water at room temperature. :Such treatment is designed to remove any oxide film on the metal. The sheets are then rinsed thoroughly in cold water and subsequently in hot water, and air dried at room temperature. The clean surface of the sheet is desirable in order to secure good bonding in the subsequent hot rolling operation.

A separation or weld-preventing material 3, consisting of a mixture of graphite in water glass, is then applied in a thin layer to selected areas on the face of sheet i according to a predetermined pattern. Such separation material may be sprayed through a masking die, painted through a stencil, squeezed through a silk screen, or applied in any other suitable manner. For instance, if the separation material 3 is to be applied through a silk screen to the selected area, graphite in the ratio of about three to four kilograms to three liters of water glass solution is satisfactory. A thinner more fluid mixture is, of

course, used if the separation material is to be applied by painting or spraying on the selected areas.

The elongation of the metal during subsequent rolling must be allowed for in the shape and dimension of the pattern of separation material originally applied to the sheet. For instance, the strip and pattern is lengthened in the direction of rolling in substantially inverse proportion to the change in thickness of the assembly. Pattern lines I0 and ii that run perpendicular to the direction of rolling are, therefore, increased in width, as indicated at [2 and I3, in substantially inverse proportion to the change in thickness of the assembly. Pattern lines 3 that run in the direction of rolling are not changed appreciably in width as indicated at 6, Figure 6. Thus, if one Wishes a conduit running perpendicular to the direction of rolling one inch in diameter and the assembly thickness during the rolling operation is reduced to one-half the original thickness, then the pattern lines running perpendicular to the direction of rolling must be made only about onehalf inch wide. The thickness of the layer of separation material decreases in direct proportion with the decrease in thickness of the assembly during rolling due to the spreading or elongation of the material during the rolling operation. The thickness of the layer of separation material after rolling should be sufficient to prevent bonding of the metal except where such bonding is desired.

After the pattern of separation material 3 has been applied to sheet I, the sheet 2 is placed on sheet I with the separation material 25 between them, Figure 3. If sheet 2 is permitted to move freely in frictional contact with the separation material on sheet I prior to the subsequent hot roll operation, the pattern is likely to be damaged or distorted so that the desired conduit system will not be obtained. The sheets are therefore fastened together to avoid obliteration of the pattern, by any suitable means, such as hell-arc welding the edges, tacking the edges together by spot-welding, or by crimping the edges, or the like.

The assembly is then placed in a furnace and heated to about 900 C. To prevent oxidation of the inner faces of the sheets i and 2, the edges of the assembly may be completely sealed as by welding or the like, or an inert or reducing atmosphere may be employed in the furnace if desired. The temperature of 900 C. is about (3. below the melting point of the alloy and is sufiiciently high to effect pressure welding of the two sheets of metal in the hot rolling step to be described hereinafter. The exact temperature to be used for pressure welding is, of course, dependent upon the melting point of the particular metal or alloy utilized and should be relatively close thereto.

Inasmuch as each sheet of the metal, i and 2, is 0.070 inch thick and the layer of separation material 3 is only about 0.002 to 0.005 inch thick, the assembly, Figure 3, is about 0.14 inch thick. As soon as the assembly has reached a temperature of about 900 C. it is hot rolled in one to a thickness of about 0.070 inch and is then cleaned with acid, washed and dried as described in the foregoing treament of sheets i and 2. It is desirable to hot roll to a reduction of thickness of at least 35% in order to insure welding of the sheets, and a reduction of approximately 50% in one pass is preferable as is described in the foregoing. The welded sheet is then cold rolled to a finish gauge of about 0.048 inch thickness, is

then annealed at a temperature of 750 C. for one half hour to remove the hardening effect of the cold rolling, and is then cleaned by acid, washing, and drying treatments as described hereinbefore. The cold rolling step is carried out in order to accurately control the thinness of the sheet. If sufficient accuracy in gauge for the particular use can be obtained by hot rolling, the entire reduction can be carried out by hot rolling, and the cold rolling and annealing treatments referred to in the foregoing may be omitted. The strength of the sheet formed by the hot rolling step is appreciably greater than that of the cast structure obtained with spot-Welding techniques. The cast structure formed by spot-welding contains appreciably larger grains than the sheet prior to such welding, Whereas the sheet formed by the hot rolling step has a grain size substantially uniform throughout the sheet.

In applying the separation material 3 to sheet I, a portion is extended to the edge of the sheet at 4. The unbounded edge 4 of sheet 9, Figure 4, is then pried open mechanically, and a copper tube is inserted into the opening and silver soldered, brazed, or threaded therein. The free end of the copper tube 1 is attached to an hydraulic pump by any suitable means such as a sleeve and nut, and about 250 to 300 pounds per square inch fluid pressure is applied to expand the metal in the unwelded inner portions of the sheet containing the separation material. Only suificient pressure need be applied to bulge the metal in these areas to an extent sufficient to provide the desired cavities or conduit indicated at 6, i2 and i3, Figures 6 and '7. As will be understood in the art the amount of fluid pressure necessary will vary with the gauge, temper, and composition of the metal used. If desired, to produce very sharp, intricate conduit patterns, the sheet Qprior to application of the pressure may be placed in a die whose faces are recessed in accordance with the desired conduit pattern. During the application of the fluid pressure, the conduit Walls 0, l2, and 13 within the die are reduced in thickness about 0.001 to 0.002 inch from the original thickness of about 0.024 inch on each side of the separation material prior to application of the fluid pressure, and appear as bulges on the surfaces of the sheet. The cavity walls are thus strengthened by the work-hardening effected by expansion of the metal.

When no die is used, the metal expands with little or no thinning of the cavity wall and the cavity is formed upon applying the fluid pressure merely by further separation or opening up of the metal. in the separation material areas with a resultant decrease of sheet length or width, or both, depending on the design and dimensionof the cavities. However, the sheet may be so held in a die, during application of the fluid pressure,

' that the length or width does not decrease and the expansion is accomplished by a thinning of the cavity Wall, as in the foregoing.

In some instances it may be desirable to have the heat exchange device in a shape other than a relatively flat sheet, for instance, a U-shaped device may be desired, such as is used to partially surround the ice cube or freezing compartment of a refrigerator. For such purpose the sheet 9 can be bent into the desired shape either before or after the fluid pressure has been applied to form the conduit within the sheet. If the bending is done after the conduits have been formed, the conduit pattern should be so designed as to permit such bending and care should be observed 6.. in such deforming operations to avoid closing off desired passageways. A hole such as illustrated at 8, Figure 6, may be drilled into the conduit and a copper tube partially inserted therein and silver soldered or brazed thereto which copper tube may then serve along with copper tube 7 to provide an entrance and exit for the heat exchange medium. The conduit 6, i2, and it, Figure 6, corresponds substantially to the pattern of separation material 3, Figure 1.

While the foregoing specific embodiment is described with particular reference to a heat exchanger, it will be understod that the expanded sheet 9, Figure 6, is relatively strong and rigid due to the ribs formed by the conduit 6, I2, and i3 and minus the inlet and outlet, 1 and 8, can be used to advantage as a sheet metal structural member. If a structural member having only longitudinal reinforcing ribs is desired, the ends of the sheet may be cut off for a sufficient distance to remove the transverse conduits, or headers, l2 and [3. The cavities in the sheet whether they be ultimately utilized for the sheet strengthening effected by their walls or as fluid conduit, or both, may as pointed out hereinbefore have practically any desired design, the design being controlled by the pattern of separation material.

For some uses, it may be desirable to have the bulges formed by the cavities all on one side of the sheet instead of on both surfaces. An embodiment illustrating such construction is shown in section in Figure 8, in which the conduit 5: and 52 forms bulges on only the top surface of the sheet. Such construction, which is well adapted for structural members having a flat or smooth face, can be obtained, for instance, if one sheet is sufficiently thicker than the other that all expansion occurs on the thin sheet surface when the fluid pressure is applied. For example, the bottom sheet I utilized may be ten times as thick as the sheet 2 and the pattern applied, the sheets assembled and hot rolled until pressure welded, and the fluid pressure applied, etc., as described in the foregoing embodiment, the final thickness of the device being greater, of course, due to the greater thickness of the bottom sheet. Such construction, as is illustrated in Figure 8, may also be obtained by inserting the rolled sheet 9 containing the separation material 3 in a die having one face recessed to conform to the conduit pattern and the other face unrecessed. Upon applying fluid pressure on the unwelded inner surfaces of sheet 9 one surface of the sheet is prevented from expanding by the unrecessed face of the die, whereas the other surface of the sheet expands into the recesses in the other face of the die. For some uses as'in structural members, a semicircular bulge or rib may not be as desirable as some other shape. The contour of the expanded surface may be controlled by providing the recesses in the die face with the desired contour. For instance, Figure 9 illustrates an embodiment for forming an angular contour instead of the semicircular contour shown for the ribs in Figure 8. The unexpanded sheet 9 containing separation material 3 is held between the unrecessed die plate I! and the die plate I6 having angular shaped recesses It in its inner face positioned over the separation material 3 within the sheet 9. Upon applying the fluid pressure, as described hereinbefore, the surface of the sheet expands forming angular contoured ribs l9, Figure 10.

of the sheet and on the opposite side of the sheet in other areas. Such an embodiment is illustrated in Figures 11 and 12, where it may be seen that the conduit is formed by expansion of the top surface towards the ends of the sheet, and by expansion of the bottom surface near the center of the sheet. Here again such construction is accomplished by inserting the sheet '9 in a die whose faces are recessed in accordance with the pattern to permit the desired expansion of the top surface near the ends of the sheet 9 forming bulge l4 and of the bottom surface at the center forming bulge IS. The conduit thus above the plane of the sheet at the end portions and below the plane of the sheet at the center portion. Where the sheet is to be shaped, for instance into a U-shape to fit about the ice-cube compartment of a refrigerator, it may be highly desirable to permit bulging of only one surface in various areas of the sheet in accordance with the practice illustrated in the foregoing.

While in the foregoing a specific rolling, annealing, and cleaning sequence is described, it will be understood that various rolling, annealing and cleaning techniques, trimming, tacking the sheets together, shaping and other such operations may be employed in accordance with this invention between the step of applying the separation material and the step of applying the fluid pressure, depending upon the prevailing practice and the physical characteristics desired the finished product. For instance, the hot and cold rolling may be carried out in a number of steps depending upon the economics of the situation and available rolling equipment, or the cold rolling or annealing, or both, may be omitted entirely. Whereas, the pressure weld is accomplished by hot rolling the assembly in accordance with the preferred practice set forth herein, it is to be understood that some metal sheeting may be pressure welded merely by applying sumcient pressure at room temperature and that such pressure welding technique may be utilized in accordance with this invention. Regardless, however, of the intermediate processing used, it is necessary that the metal of the sheets be suitably joined to form one substantially uniform layer at all superposed points not held apart by the separation material prior to application of the fluid pressure.

The process is well suited for continuous operation. For example, the patterns of the separation material may be applied successively to the surface of a strip of metal being unwound from a coil, a second strip of metal being unwound from another coil may be superposed on the pattern-coated strip, and the strips then tacked together by spot-welding, edge crimping, or the like and fed continuously through a heating furnace and hot rolling mill. After the rolling and other such processing has been completed, the pressure welded strip containing the separation material is then expanded by applying fluid pressure as described above to the internal metal surfaces coated with separation material.

Any suitable separation material may be employed, its chief function being to prevent bond-- ing of the coated surfaces during the welding operation. For instance, in addition to the graphite water glass mixture set forth in the foregoing, other inorganic ingredients mixtures may be employed such as zinc oxide, k-ieselguhr or other diatomaceous earths, flint, talc, powdered quartz, clays, and the like and mixtures thereof with each other and with graphite and water glass or the like. The separation material used must, of course, be so compounded as to flow or elongate with the metal and retain uniformly sufficient thickness to prevent bonding where not desired. Likewise, although the embodiment is described in the foregoing with particular reference to copper base alloys, the process of this invention is applicable to other metal sheeting, for example, aluminum, magnesium, steel, and the like adapted to be pressure welded. As will be apparent from the foregoing, the process of this invention permits the fabrication of a sheet of metal provided with internal ducts or internal passageways of substantially any desired design or pattern, which oavitied sheet of metal with appropriate conduit pattern is adapted for use as a lower cost, more efficient heat exchange device than is obtainable with prior processes. Relatively thick low cost sheet stock may be employed since the desired cavity wall thinness is obtained by the thinning action resulting from the pressure welding step and the thinning of the metal in the immediate area upon which the fluid pressure is applied. In prior methods, in which the cavity wall was stamped or drawn, the sheet stool: used had to be substantially of the thinness desired in the cavity wall. Likewise, the process permits the manufacture of cavitied sheet metal well suited for strong li ht weight structural members and other uses. It is to be understood that the embodiment of the present invention as shown and described is only illustrative and that many changes may be made therein without departing from the spirit and scope of the invention as set forth in the following claims.

The word sheet is used in the appended claims to define a piece of metal which is very thin in relation to its length and breadth.

Having thus described the invention what is claimed and desired to secure by Letters Patent is:

1. The method of making hollow sheet metal fabrications having a plurality of interconnected passageway portions in the form of a single sheet of homogeneous metal which consists essentially of interposing a pattern composed of separation material between two clean-surfaced metal sheets, which pattern has the general configuration of the desired pattern of passageway portions but is foreshortened in one direction and includes a plurality of spaced, relatively narrow, elongated, interconnected passageway portions arranged to define between them a, plurality of spaced areas free from separation material in which the sheets are to be Welded together; securing said plates together at portions other than those portions opposite the pattern of separation material to prevent relative slippage during a subsequent rolling operation; uniformly reducing the thickness of the assembly by at least 35%, elongating the assembly in the direction in which the pattern of separation material is foreshortened to extend the pattern of separation material and the area of the sheets between said passageway portions in that direction without appreciable extension of the pattern of the separation material or the areas of the sheets between said passageway portions in a transverse direction and welding the contacting inner surfaces of the sheets in the areas surrounding the pattern of separation material and between said spaced passageway portions, all, and simultaneously, by hot rolling the assembly in the di- 2. The method of claim 1 in which the hot.

rolling of the assembly is such as to reduce the thickness thereof by at least 50%.

3. The method of claim 1 in which the interconnected passageway portions of the separation material include at least one elongated area and a plurality of transversely-extending areas.

4. The method of claim 1 in which the sheet resulting from the hot rolling operation is placed between a pair of spaced confining die faces having portions at least opposite the pattern of the separation material which are spaced apart a distance substantially greater than the thickness of the resulting sheet; and the fluid forces the metal opposite the separation material into contact with at least one of the adjacent faces of the confining dies with suficient force to cause the metal contacting said face to assume the shape of said face at the places of contact therewith.

5. The method of claim 1 in which the sheet 10 metal fabrication is a heat-exchanger element and an outlet from said passageways is formed at a place remote from the inlet.

References Cited in the file of this patent UNITED STATES PATENTS I Number Name Date Re. 19,778 Litle, Jr. Dec. 3, 1935 346,661 Knight Aug. 3, 1886 361,857 Bigney Apr. 26, 1887- 1,'709,865 Muffiy Apr. 23, 1929 1,712,085 Litle, Jr. May 7, 1929 1,723,659 Rosenqvist Aug. 6, 1929 1,798,652 Booth Mar. 31, 1931 2,034,278 Becket Mar. 17, 1936 2,154,216 Savage Apr. 11, 1939 2,161,293 Heath June 6, 1939 2,212,481 Sendzimir Aug. 20, 1940 2,312,451 Strike Mar. 2, 1943 2,458,629 Orley Jan. 11, 1949 2,472,937 Brinkoeter June 14, 1949 2,498,275 Johnson Feb. 21, 1950 2,582,358 Schoellerman Jan. 15, 1952 2,585,736 Burr Feb. 12, 1952 FOREIGN PATENTS Number Country Date 401,476 Germany Sept. 8, 1924 94,212 Sweden Jan. 13, 1939 

